The present invention relates to positioning systems, and particularly to such systems for selectively positioning a device along up to three axes.
Two-axes positioning systems are frequently used in X-Y plotters, and three-axes positioning systems are frequently used in three-dimensional conveyors for conveying articles to preselected locations in space. Two-axes positioning systems commonly include an X-carriage driven along the X-axis by one drive, and a Y-carriage driven along the Y-axis by a separate drive, the object to be positioned being carried by the Y-carriage. Where the object is also to be positioned along the Z-axis, a separate drive is usually provided on one of the carriages for this purpose. Where closed-loop flexible couplings are used in the drives, a separate closed-loop is usually provided for each drive.
Such known positioning systems have a number of drawbacks. Thus, providing a separate drive for each axis increases the initial and maintenance costs in proportion to the number of axes. In addition, where closed loop couplings (e.g., cord, wire or belt) are used, special provisions are usually required either to maintain a constant tension in the separate closed loops, or else to provide compensation for any such changes in tension, which further increases the initial and maintenance costs of the system.